Ceramic circuit board and process for producing same

ABSTRACT

According to one embodiment, a ceramic circuit board includes a ceramic substrate, a copper circuit plate and a brazing material protrudent part. The copper circuit plate is bonded to at least one surface of the ceramic substrate through a brazing material layer including Ag, Cu, and Ti. The brazing material protrudent part includes a Ti phase and a TiN phase by 3% by mass or more in total, which is different from the total amount of a Ti phase and a TiN phase in the brazing material layer that is interposed between the ceramic substrate and the copper circuit plate. The number of voids each having an area of 200 μm 2  or less in the brazing material protrudent part is one or less (including zero).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of PCT Application No.PCT/JP2010/065914, filed Sep. 15, 2010 and based upon and claiming thebenefit of priority from prior Japanese Patent Application No.2009-213511, filed Sep. 15, 2009, the entire contents of all of whichare incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a ceramic circuit boardand a method for the production of the same, and is specificallypreferable for a power module and the like that require highreliability.

BACKGROUND

In recent years, power modules are used so as to control a large currentand a large voltage in electrical vehicles and electrical trains fromthe viewpoints of improvement of performances of industrial devices andproblems of the global environment. The heat produced by semiconductordevices that are mounted on them has been increasing steadily.Therefore, a heat releasing property is important in circuit boards forpower modules. Ceramic-metal bonded circuit boards using ahigh-thermal-conduction ceramic substrate bonded to a metal plate ofcopper, aluminum or the like are widely used.

For high-thermal-conduction ceramic substrates, substrates of siliconnitride or aluminum nitride having a high thermal conduction propertyand high electrical insulation property are used. A ceramic-metalcircuit boards including the high-thermal-conduction ceramic substratebonded to a metal plate with an active brazing metal comprising Ag—Cuare widely used. As the metal plate, copper, which is superior toaluminum in electrical conductivity and thermal conduction property, isgenerally used. Since copper has a higher yield stress than doesaluminum and differs greatly from ceramic in thermal expansion, there isa problem that the thermal cycle resistance and thermal shock resistanceof the ceramic-metal circuit board are decreased and cracks are easilyproduced in the ceramic substrate as the thickness of the copper plateincreases, which leads to a decrease in reliability.

The above-mentioned problems were reported in Patent Literatures 1, 2and the like. In Patent Literatures 1 and 2, reliability is improved byrelaxing stress concentration at the end surface portion of a coppercircuit plate in the ceramic substrate by making a brazing materiallayer protrude outward from the copper circuit plate.

In a ceramic-metal circuit board, a predetermined circuit pattern isformed on a copper circuit plate so as to mount and connect asemiconductor device. High-definition is required for the position andform of the circuit pattern, and in order to obtain a high-definitionpattern, a method comprising bonding a copper plate to a ceramicsubstrate and thereafter forming a circuit pattern by an etching processis generally used.

CITATION LIST Patent Literatures

-   Patent Literature 1: Jpn. Pat. Appln. KOKAI Publication No.    10-190176-   Patent Literature 2: Jpn. Pat. Appln. KOKAI Publication No.    11-340598

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view that schematically shows a firstmasking step in a second embodiment;

FIG. 2 is a cross-sectional view that schematically shows the steps ofapplying and printing the brazing material in the second embodiment;

FIG. 3 is a cross-sectional view that schematically shows the step oflaminating the copper plate in the second embodiment;

FIG. 4 is a cross-sectional view that schematically shows a secondmasking step in the second embodiment;

FIG. 5 is a cross-sectional view that schematically shows the step ofetching in the second embodiment;

FIG. 6 is a cross-sectional view that schematically shows the ceramiccircuit board of the first embodiment; and

FIG. 7 is an optical micrograph of a cross-sectional surface obtained bycutting a copper circuit plate of a circuit board of sample 17 in athickness direction.

DETAILED DESCRIPTION

In general, according to one embodiment, a ceramic circuit boardincluding a ceramic substrate, a copper circuit plate and a brazingmaterial protrudent part is provided. The copper circuit plate is bondedto at least one surface of the ceramic substrate through a brazingmaterial layer including Ag, Cu, and Ti. The brazing material protrudentpart is formed by the brazing material layer which protrudes outwardfrom a side surface of the copper circuit plate. The brazing materialprotrudent part includes a Ti phase and a TiN phase by 3% by mass ormore in total, which is different from the total amount of a Ti phaseand a TiN phase in the brazing material layer that is interposed betweenthe ceramic substrate and the copper circuit plate. The number of voidseach having an area of 200 μm² or less in the brazing materialprotrudent part is one or less (including zero).

According to one embodiment, a method for the production of a ceramiccircuit board is provided. The method includes:

providing a first masking on a part other than an area to be a coppercircuit pattern and a brazing material protrudent part on a ceramicsubstrate;

forming a brazing material layer comprising Ag, Cu and Ti on an areaother than the first masking on the ceramic substrate;

mounting a copper plate on the brazing material layer and bonding theceramic substrate and the copper plate by heating;

providing a second masking on an area to be a copper circuit pattern onthe copper plate; and

forming a copper circuit pattern by etching.

The present inventors have ascertained that, when a brazing materiallayer that protrudes outward from the copper circuit plate is provided,there is a problem that voids are produced in the brazing material layerthat protrudes from the copper circuit plate. The voids are produced inthe case when the protrudent part and a circuit pattern are formed by anetching process. Therefore, uniform dispersion of thermal stress that isto be relaxation of the stress concentration at the end portion of thecopper circuit plate, which can be expected by protruding the brazingmaterial layer, is not caused, and cracking of the ceramic substrateeasily occurs.

The embodiment was made in view of such technical problems, and aims atproviding a ceramic circuit board that has a brazing material protrudentpart having fewer defects due to voids or the like, and has improvedthermal cycle resistance, and a method for the production of the same.

According to the embodiment, a ceramic circuit board that has a brazingmaterial protrudent part having fewer defects due to voids or the likeand has improved thermal cycle resistance, and a method for theproduction of the same can be provided.

First Embodiment

The ceramic circuit board of the first embodiment comprises a ceramicsubstrate, a copper circuit plate that is bonded to at least one surfaceof the ceramic substrate through a brazing material layer, and a brazingmaterial protrudent part that is formed by the brazing material layerand protrudes outward from the side surface of the copper circuit plate.The brazing material layer is formed from a brazing material comprisingAg, Cu and Ti. The present inventors have discovered that aceramic-metal circuit board having high reliability can be realized byadjusting the brazing material protrudent part to comprise a Ti phaseand a TiN phase by 3% by mass or more in total, and adjusting the totalamount thereof to be different from the total amount of a Ti phase and aTiN phase in the brazing material layer that is interposed between thecopper circuit plate and the ceramic substrate (hereinafter referred toas a bonding layer), and further adjusting the number of voids eachhaving an area of 200 μm² or less in the brazing material protrudentpart to one or less (including zero), since the thermal stress due tothe difference in thermal expansion between the copper circuit plate andan electronic part is relaxed and bonding defects are decreasedextremely.

Here, the interface between the bonding layer and the ceramic substrateor copper circuit plate is determined by the distribution of Ag, and theinterface is defined by using a part in which Ag is present as a bondinglayer. Furthermore, the number of voids each having an area of 200 μm²or less can be obtained by measuring the voids in a cross-sectionalsurface having an area of 200 μm² in the brazing material protrudentpart.

It is desirable that the total of the Ti phase and TiN phase in thebrazing material protrudent part is more than the total of the Ti phaseand TiN phase in the bonding layer. This can further increase an effectof relaxing thermal stress.

It is more preferable that the brazing material protrudent partcomprises the Ti phase and TiN phase by 3% by mass to 40% by mass intotal. When the total of the Ti phase and TiN phase exceeds 40% by mass,the amount of the Ti phase and TiN phase becomes too much, thereby thebrazing material protrudent part becomes hard and may lead to decreasein thermal cycle characteristics (TCT characteristics).

The total amount of the Ti phase and TiN phase in the brazing materiallayer can be measured by, for example, an electron probe microanalysis(EPMA) or an energy dispersive X-ray analysis (EDX).

It is preferable that the brazing material layer is formed by using abrazing material having a composition consisting of Ag: 90 to 50% byweight, an element consisting of Sn and/or In: 5 to 15% by weight, Ti:0.1 to 6% by weight, a remnant Cu and unavoidable impurities. When thecomposition is such composition, a sufficient effect can be obtained. Itis preferable that the content of Ti is from 2 to 5% by weight. Theabove-mentioned composition is the composition of the brazing materialbefore application and printing on the ceramic substrate, and thecomposition of the bonding layer after bonding varies depending on astep of binding an active metal (heat treatment) that is conducted afterthe steps of application and printing, and the like.

It is preferable that the brazing material protrudent part has aprotrudent length that is 0.01 mm or more and is 30% or less of a spacein the copper circuit plate. By adjusting the protrudent length to 0.01mm or more, the effect of relaxing stress concentration by the brazingmaterial protrudent part can be obtained sufficiently. By adjusting theprotrudent length to 30% or less of the space in the copper circuitplate, the electrical insulation property between copper circuit platescan be ensured, and formation of fine patterns can be accommodated. Amore preferable range of the protrudent length is from 0.01 to 20% ofthe space in the copper circuit plate.

The ceramic substrate can be formed from, for example, silicon nitride(Si₃N₄), aluminum nitride (AlN) or alumina (Al₂O₃). A silicon nitridesubstrate is preferred since a ceramic circuit board that is excellentin both thermal cycle resistance and thermal shock resistance can beobtained.

Particularly, a silicon nitride (Si₃N₄) substrate having a thermalconduction rate of 80 W/m·K or more and a three-point bending strengthof 600 MPa or more is preferred. Furthermore, an aluminum nitride (AlN)substrate having a thermal conduction rate of 150 W/m·K or more and athree-point bending strength of 400 MPa or more is preferred.Furthermore, an alumina (Al₂O₃) substrate having a thermal conductionrate of 20 W/m·K or more and a three-point bending strength of 400 MPaor more is preferred.

The copper circuit plate is formed from copper or a copper alloy. Thecopper circuit plate preferably has a thickness of 0.25 mm or more. Thisis because the thicker the copper circuit plate is, the greater thestresses produced in the ceramic substrate and the end portion of thecopper circuit plate are, and thus stress relaxation by the brazingmaterial protrudent part is required. More preferably, the coppercircuit plate has a thickness of from 0.25 mm to 0.8 mm. When thethickness of the copper circuit plate exceeds 0.8 mm, the stressproduced between an electronic part that is mounted on the coppercircuit plate by soldering and the copper circuit plate increases, andthe effect by the brazing material protrudent part may not be obtainedsufficiently.

In order to obtain a sufficient effect of improving thermal cycleresistance, it is desirable that the ceramic substrate is formed fromsilicon nitride, aluminum nitride or alumina and the thickness of thecopper circuit plate is adjusted to 0.25 mm or more.

Second Embodiment

As a method for the production of a ceramic circuit board of the firstembodiment, a method for the production of a second embodiment is shownas an example.

The method of the second embodiment comprises: a step of providing afirst masking on a part other than an area to be a copper circuitpattern and a brazing material protrudent part on a ceramic substrate; astep of forming a brazing material layer by applying or printing abrazing material comprising Ag, Cu and Ti to the area on which the firstmasking has not been provided; a step of mounting a copper plate on thebrazing material layer and bonding the ceramic substrate and the copperplate by heating; a step of providing a second masking on an area to bea copper circuit pattern of the copper plate; and a step of forming acopper circuit pattern by etching.

Hereinafter the production method will be explained with referring toFIGS. 1 to 6.

As shown in FIG. 1, a first masking 2 is provided on a ceramic substrate1. The first masking 2 is formed on a part other than an area 3 to be acopper circuit pattern and a brazing material protrudent part. When thefirst masking 2 is not formed, conduction due to the brazing materialthat is protruding excessively to the space in the copper circuit mayoccur, and thus the brazing material protrudent part should be etched byhydrofluoric acid or an alkali liquid for removing brazing materials.The present inventors have found out that voids are produced in thebrazing material protrudent part by the etching, thereby uniformdispersion of thermal stress that is to be the relaxation of the stressconcentration at the end portion of the copper circuit plate is notcaused, and cracking of the ceramic substrate and the like easilyoccurs. By conducting the first masking step, the etching of the brazingmaterial protrudent part becomes unnecessary, thereby pores in thebrazing material protrudent part can be decreased and formation of largepores can be prevented.

Next, as shown in FIG. 2, a brazing material 4 comprising Ag, Cu and Tiis printed on or applied to the area 3 on which the first masking hasnot been provided. The area of the brazing material layer 4 to beprinted or applied is adjusted to be larger than the shape of the coppercircuit plate by a length of protruding. As the method for protruding isnot limited to the method comprising printing or applying the brazingmaterial in advance to be larger than the shape of the copper circuitplate by a length of protruding, and for example, a method comprisingprinting or applying the brazing material in the same shape as the shapeof the copper circuit plate and protruding the brazing material bybonding can be adopted. Furthermore, the thickness of the brazingmaterial layer is preferably from 10 to 40 μm. When the thickness isless than 10 μm, a sufficient bonding strength may not be obtained,whereas when it exceeds 40 μm, a further effect cannot be obtained, andthe cost may be increased.

As shown in FIG. 3, a copper plate 5 is mounted on the brazing materiallayer 4, and the ceramic substrate and the copper plate are bound byheating (an active metal brazing process). As for the conditions for theactive metal brazing, an inert atmosphere such as in vacuum and anitrogen atmosphere, a temperature of from 700 to 900° C., and heatingfor 10 to 120 minutes are desirable. By this active metal brazing, a Tiphase and a TiN phase are produced in the brazing material layer 4. Thedegree of production can be adjusted by the composition of the brazingmaterial used, the conditions for the active metal brazing, and thelike. When the ceramic substrate is a nitride ceramic substrate (AlN,Si₃N₄ and the like), the adjustment is conducted in view of that the TiNphase is formed by a reaction between the Ti in the brazing material andthe nitrogen in the nitride ceramic substrate.

It is desirable that markings for position alignment are provided to theceramic substrate 1 and the copper plate 5. For example, a hole orgroove for position alignment can be formed on the ceramic substrate 1and a protrusion that corresponds to the hole or groove can be providedto the copper plate 5.

Next, as shown in FIG. 4, a second masking 6 is provided on the copperplate 5 on the area to be a copper circuit pattern. Thereafter, as shownin FIG. 5, a portion 7 on which the second masking 6 has not been formedon the copper plate 5 is removed by etching to form a copper circuitpattern. As an etchant, an etchant for copper plate etching can be used,and specific examples may include ferric chloride, cupric chloride andthe like. Since an etchant for copper plate etching is used, when thebrazing material protrudent part is exposed excessively to the etchant,the Cu in the brazing material is etched. This phenomenon leads topores.

The first and second maskings 2 and 6 are then removed, thereby theceramic circuit board 8 of the first embodiment as shown in FIG. 6 canbe obtained. The first and second maskings can be formed from aprintable organic ink resist or the like.

During the above-mentioned etching, a part of the Cu component in abrazing material layer 4 a that protrudes outward from the side surfaceof the copper circuit pattern 5 (brazing material protrudent part) isremoved together, and thus the ratio of the total amount of the Ti phaseand TiN phase in the brazing material protrudent part 4 a with respectto the entirety of the brazing material protrudent part 4 a isincreased. On the other hand, the composition of the brazing materiallayer (bonding layer) 4 b that is interposed between the copper circuitpattern 5 and the ceramic substrate 1 is not affected by the etching.Therefore, the total of the Ti phase and TiN phase in the brazingmaterial protrudent part 4 a is increased to 3% by mass or more, and isdifferent from the total amount of the Ti phase and TiN phase in thebonding layer 4 b. Furthermore, since the etching is for forming thecopper circuit pattern, it is not necessary to expose excessively thebrazing material protrudent part 4 to the etchant, and thus voids arenot produced in the brazing material protrudent part 4 a and the numberof voids each having an area of 200 μm² or less in the brazing materialprotrudent part 4 a becomes one or less (including zero). Needless tosay, voids having an area exceeding 200 μm² are not present.

The total amount of the Ti phase and TiN phase in the brazing materialprotrudent part 4 a can be adjusted by the length of the brazingmaterial protrudent part, conditions for etching, and the like.Furthermore, the number of voids each having an area of 200 μm² or lesscan be adjusted by conditions for etching, and the like. For example,adjusting the concentration of ferric chloride or cupric chloride in theetchant to be small as 15 wt % or less, and the like may be exemplified.While the lower limit of the concentration of ferric chloride or cupricchloride in the etchant is not specifically limited, it is preferably 5wt % or more since etching proceeds slowly and the production timebecomes longer when the concentration is too small. The shape of thebrazing material protrudent part 4 a is not limited to have a R-shape inthe cross section shown in FIG. 6 and may have a rectangular shape inthe cross section.

Furthermore, it is preferable that the end surface of the copper circuitpattern 5 after the etching treatment has a R-shape in the crosssection, a sloping shape (a descending slope toward the side of thebrazing material layer 4 from the upper surface of the copper circuitpattern 5, for example, a foot shape like the foot of Mt. Fuji). By suchshape, the stress at the end surface of the copper circuit plate isrelaxed easily.

EXAMPLES

Hereinafter the embodiments will be explained more specifically.

(Samples 1 to 9)

The respective samples were prepared according to the method explainedbelow. First, first masking was conducted on the surface on which acopper circuit pattern was to be formed, the surface being of a ceramicsubstrate of 50×60 mm. The first masking was conducted on an area excepton an area having a predetermined size to be a copper circuit patternand a brazing material protrudent part. Next, an Ag—Cu—Ti-based brazingmaterial (Ag: 67% by weight; Cu: 20% by weight; Sn: 10% by weight; Ti:3% by weight) was printed by a thickness of 15 μm on the area on whichthe first masking had not been formed and was also printed on the backsurface by a thickness of 15 μm, and copper plates were disposed on theboth surfaces of the ceramic substrate and bound to the ceramicsubstrate by heating in vacuum at 10⁻³ Pa and 800° C. for 40 minutes. Asfor the copper circuit plate, two copper plates of 20×20 mm weredisposed at a space of 1 mm.

Next, a second masking (etching resist) having a patterned shape wasprinted on the copper plates, an etching treatment was conducted byusing a ferric chloride liquid (concentration of ferric chloride: 5 to15 wt %) to form a circuit pattern, and the resist was peeled off togive a circuit board. The thicknesses of the AlN substrate used insamples 1 and 2 and Al₂O₃ substrate used in samples 3 and 4 were both0.635 mm, and the thickness of the Si₃N₄ substrate used in samples 5 to9 was 0.32 mm. Furthermore, the AlN substrate used was one having athermal conduction rate of 170 W/m·K and a three-point bending strengthof 450 MPa; the Al₂O₃ substrate used was one having a thermal conductionrate of 25 W/m·K and a three-point bending strength of 450 MPa; and theSi₃N₄ substrate used was one having a thermal conduction rate of 90W/m·K and a three-point bending strength of 700 MPa.

The thickness of the copper circuit plate, the kind of the material forthe ceramic substrate, the amount of protrusion outward from the sidesurface of the copper circuit plate (unit: mm, a ratio when the space inthe copper circuit is 100%), the total amount of the Ti phase and TiNphase in the bonding layer, the total amount of the Ti phase and TiNphase in the protruded brazing material, and the number of voids eachhaving an area of 200 μm² or less in the protruded brazing material, areshown in the following Table 1.

Furthermore, defective bonding and deficiency in brazing were examinedby visual observation and ultrasonic flaw detection for the obtainedceramic circuit boards, and thermal cycle tests were conducted by using−50° C., 30 minutes→room temperature, 10 minutes→155° C., 30minutes→room temperature, 10 minutes as one cycle. For the circuitboards after the test, the presence or absence of abnormalities such aspeeling of the circuit plates, cracking of the ceramic substrate, andthe like, was examined by visual observation and ultrasonic flawdetection. The results by the examination are shown in the followingTable 1.

TABLE 1 Ratio of Total amount of Number of voids brazing material Totalamount Ti phase and TiN each having area Thickness Length of protrudentof Ti phase phase in brazing of 200 μm or of copper Kind of brazingmaterial part to space and TiN phase material less in brazing Thermalcircuit ceramic protrudent in copper circuit in bonding layer protrudentpart material resistance Sample board (mm) substrate part (mm) plate (%)(% by mass) (% by mass) protrudent part cycle (cycles) 1 0.4 AlN 0.01 110 16 0 300 2 0.4 AlN 0.12 12 5 35 1 400 3 0.4 Al₂O₃ 0.03 3 7 10 1 300 40.4 Al₂O₃ 0.02 2 7 30 0 400 5 0.6 SI₃N₄ 0.05 5 3 5 1 3000 6 0.6 SI₃N₄0.08 8 5 28 0 5000 7 0.8 SI₃N₄ 0.03 3 5 10 0 2000 8 0.8 SI₃N₄ 0.01 1 720 0 3000 9 0.8 SI₃N₄ 0.20 20 7 40 1 3500

From the results of sample 1 and sample 2 using the AlN substrate, it isunderstood that samples 1 and 2 in which the total amount of the Tiphase and TiN phase in the protruded brazing material is 3% by mass ormore and is different from the total amount of the Ti phase and TiNphase in the bonding layer, and the number of voids each having an areaof 200 μm² or less in the protruded brazing material is one or less, areexcellent in thermal cycle resistance.

From the results of sample 3 and sample 4 using the Al₂O₃ substrate, itis understood that samples 3 and 4 in which the total amount of the Tiphase and TiN phase in the protruded brazing material is 3% by mass ormore and is different from the total amount of the Ti phase and TiNphase in the bonding layer, and the number of voids each having an areaof 200 μm² or less in the protruded brazing material is one or less, areexcellent in thermal cycle resistance.

From the results of samples 5 to 9 using the Si₃N₄ substrate, it isunderstood that samples 5 to 9 in which the total amount of the Ti phaseand TiN phase in the protruded brazing material is 3% by mass or moreand is different from the total amount of the Ti phase and TiN phase inthe bonding layer, and the number of voids each having an area of 200μm² or less in the protruded brazing material is one or less, areexcellent in thermal cycle resistance. In addition, voids each having anarea exceeding 200 μm² were not present in samples 1 to 9. Furthermore,the end surface of the copper circuit plate had an inclined shape (afoot shape) in samples 1 to 9.

Comparative Example 1

An Ag—Cu—Ti-based brazing material that was the same as that used insamples 1 to 9 was applied to the entire surface of a ceramic substrate(AlN substrate) by a thickness of 15 μm, and a copper plate was bondedthereon and thermally bonded. Thereafter, the copper plate was etchedwith ferric chloride in a patterned form, and the protruded brazingmaterial was further etched using hydrofluoric acid. The amount ofprotrusion was 0.12 mm that was the same as that in sample 2. The numberof voids each having an area of 200 μm² or less in the protruded brazingmaterial was counted and found to be eight. Furthermore, the samethermal cycle test as that in samples 1 to 9 was conducted, and it wasfound to be 340 cycles.

(Samples 11 to 15)

Using an active metal brazing material comprising 63% by weight of Ag,32% by weight of Cu and 5% by weight of Ti, ceramic circuit boards eachhaving a copper plate and a silicon nitride substrate (plate thickness:0.32 mm) that had been bonded were produced. The masking and activemetal brazing were conducted under the same conditions as thoseexplained in samples 1 to 9.

The thickness of the copper circuit plate, the kind of the material forthe ceramic substrate, the amount of protrusion outward from the sidesurface of the copper circuit plate (unit: mm, a ratio when the space inthe copper circuit is 100%), the total amount of the Ti phase and TiNphase in the bonding layer, the total amount of the Ti phase and TiNphase in the protruded brazing material, and the number of voids eachhaving an area of 200 μm² or less in the protruded brazing material, areshown in the following Table 2.

Furthermore, the numbers of thermal cycle resistance that were measuredby conducting the same thermal cycle tests as those explained in samples1 to 9 are shown in Table 2.

TABLE 2 Ratio of Total amount of Number of voids brazing material Totalamount Ti phase and TiN each having area Thickness Length of protrudentof Ti phase phase in brazing of 200 μm or of copper Kind of brazingmaterial part to space and TiN phase material less in brazing Thermalcircuit ceramic protrudent in copper circuit in bonding layer protrudentpart material resistance Sample board (mm) substrate part (mm) plate (%)(% by mass) (% by mass) protrudent part cycle (cycles) 11 0.3 SI₃N₄ 0.033 6 29 1 5000 or more 12 0.3 SI₃N₄ 0.09 9 10 37 0 5000 or more 13 0.5SI₃N₄ 0.02 2 8 22 0 4000 14 0.5 SI₃N₄ 0.1 10 10 34 0 5000 or more 15 0.5SI₃N₄ 0.12 12 6 29 0 5000 or more

From the results in Table 2, it is understood that samples 11 to 15 inwhich the total amount of the Ti phase and TiN phase in the protrudedbrazing material is 3% by mass or more and is different from the totalamount of the Ti phase and TiN phase in the bonding layer, and thenumber of voids each having an area of 200 μm² or less in the protrudedbrazing material is one or less, are excellent in thermal cycleresistance, even in the cases when the composition of the active metalbrazing material is changed. Furthermore, in the case when siliconnitride was used as a ceramic substrate, no bonding defect was present,no crack was observed between the ceramic substrate and the end portionof the copper circuit plate, and the thermal shock resistance wasexcellent, even after 3,000 heat cycles. In addition, voids each havingan area exceeding 200 μm² were not present in samples 11 to 15.Furthermore, the end surface of the copper circuit plate had an inclinedshape (a foot shape) in samples 11 to 15.

(Samples 16 to 19)

First masking was conducted on the surface on which a copper circuitpattern was to be formed, the surface being of a silicon nitride (Si₃N₄)substrate of 40×60×0.32 mm. The first masking was conducted on an areaexcept on an area having a predetermined size to be a copper circuitpattern and a brazing material protrudent part. Next, an Ag—Cu—Ti-basedbrazing material was printed on the area on which the first masking hadnot been formed and was also printed on the back surface, and copperplates were disposed on the both surfaces of the silicon nitridesubstrate and bound to the silicon nitride substrate by heating invacuum at 10⁻³ Pa and 760 to 810° C. for 20 to 50 minutes. As for thecopper circuit plate, two copper plates of 15×20×0.3 mm were disposed ata space of 1 mm. The composition of the Ag—Cu—Ti-based brazing materialand the thickness of the brazing material layer were as shown in Table3. As the silicon nitride (Si₃N₄) substrate, one having a thermalconduction rate of 85 W/m·K and a three-point bending strength of 750MPa was used.

Next, a second masking (etching resist) in a patterned form was printedon the copper plate, and an etching treatment was conducted using acupric chloride liquid (the concentration of cupric chloride: 5 to 15 wt%) to form a circuit pattern, and the resist was peeled off to give acircuit board.

The same measurements as those for sample 1 were conducted for theobtained silicon nitride circuit board. The results are shown in Table4.

TABLE 3 Composition of Ag—Cu—Ti Thickness of brazing Sample brazingmaterial (wt %) material layer (μm) 16 Ag(68), Cu(25), In(5), Ti(2) 4017 Ag(60), Cu(25), In(10), Ti(5) 40 18 Ag(68), Cu(29), Ti(3) 20 19Ag(60), Cu(22), Sn(15), Ti(3) 10

TABLE 4 Total amount of Number of voids Ratio of Total amount Ti phaseand TiN each having area Length of brazing material of Ti phase phase inbrazing of 200 μm or brazing material protrudent and TiN phase materialless in brazing Thermal protrudent part to space in in bonding layerprotrudent part material resistance Sample part (mm) copper plate (%) (%by mass) (% by mass) protrudent part cycle (cycles) 16 0.01 1 3 38 05000 or more 17 0.05 2 6 35 0 5000 or more 18 0.10 10 4 18 0 5000 ormore 19 0.15 15 4 10 0 5000 or more

As understood from Table 3 and Table 4, it was confirmed that excellentproperties were shown even if the composition of the brazing materialand the thickness of the brazing material layer were changed.Furthermore, since a silicon nitride substrate was used, no bondingdefect was present, no crack was observed between the silicon nitridesubstrate and the end portion of the copper circuit plate, and thethermal shock resistance was excellent, even after 5,000 heat cycles. Inaddition, voids each having an area exceeding 200 μm² were not presentin samples 16 to 19. Furthermore, as shown in the optical micrograph ofthe cross-sectional surface in the thickness direction of the coppercircuit plate 5 in FIG. 7, the copper circuit plate 5 had an end surfacehaving an inclined shape (a foot shape). The same shape was alsoobserved in other samples.

As explained above, according to the embodiments and Examples, a ceramiccircuit board having high reliability can be formed, which issignificantly effective in industries.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

1. A ceramic circuit board, comprising: a ceramic substrate, a coppercircuit plate bonded to at least one surface of the ceramic substratethrough a brazing material layer comprising Ag, Cu, and Ti, and abrazing material protrudent part formed by the brazing material layerwhich protrudes outward from a side surface of the copper circuit plate,wherein the brazing material protrudent part comprises a Ti phase and aTiN phase by 3% by mass or more in total, which is different from thetotal amount of a Ti phase and a TiN phase in the brazing material layerthat is interposed between the ceramic substrate and the copper circuitplate, and a number of voids each having an area of 200 μm² or less inthe brazing material protrudent part is one or less (including zero). 2.The ceramic circuit board according to claim 1, wherein the brazingmaterial protrudent part comprises the Ti phase and TiN phase by from 3%by mass to 40% by mass in total.
 3. The ceramic circuit board accordingto claim 1, wherein the brazing material protrudent part has aprotrudent length that is 0.01 mm or more and is 30% or less of a spacein the copper circuit plate.
 4. The ceramic circuit board according toclaim 1, wherein the ceramic substrate is composed of silicon nitride,aluminum nitride or alumina, and the copper circuit plate has athickness of 0.25 mm or more.
 5. The ceramic circuit board according toclaim 1, wherein the brazing material layer is formed using a brazingmaterial having a composition consisting of Ag: 90 to 50% by weight, anelement consisting of Sn and/or In: 5 to 15% by weight, Ti: 0.1 to 6% byweight, a remnant Cu and unavoidable impurities.
 6. A method for theproduction of a ceramic circuit board, comprising: providing a firstmasking on a part other than an area to be a copper circuit pattern anda brazing material protrudent part on a ceramic substrate; forming abrazing material layer comprising Ag, Cu and Ti on an area other thanthe first masking on the ceramic substrate; mounting a copper plate onthe brazing material layer and bonding the ceramic substrate and thecopper plate by heating; providing a second masking on an area to be acopper circuit pattern on the copper plate; and forming a copper circuitpattern by etching.
 7. The method for the production of a ceramiccircuit board according to claim 6, wherein an etchant of ferricchloride or cupric chloride is used in the etching.
 8. The method forthe production of a ceramic circuit board according to claim 6, whereinmarkings for position alignment are provided to the ceramic substrateand the copper plate.
 9. The method for the production of a ceramiccircuit board according to claim 6, wherein a material for the firstmasking and second masking is a printable organic ink resist.